Not sure if they are supposed to do this, but I have noticed since using them that they form a little indented circle in the middle of the cap (akin to a snapple or lipton iced tea top) when you cap them that I never noticed when using other bottle caps.

I just buy the "regular" caps since they're like 1/2 the price at my LHBS vs the O2 absorbing caps. I'm having a hard time seeing how they could be an advantage if you're bottle conditioning. Wouldn't the yeast eat whatever O2 you might introduce during bottling? I guess if you're bottling from a keg the caps might make a small difference. In any case, after they're capped, the bottles aren't 100% sealed. They can still allow air to get in, albeit very very very slowly.

Get about 2000 of them and close yourself in a small room then wet them. If you can't breathe, then they are the right ones.

Are people putting these caps on without sanitizing? I'm not crazy about that idea but there's talk if you sanitize them, then by the time you put them on the bottle, they have lost their O2 absorbing ability.

I just buy the "regular" caps since they're like 1/2 the price at my LHBS vs the O2 absorbing caps. I'm having a hard time seeing how they could be an advantage if you're bottle conditioning. Wouldn't the yeast eat whatever O2 you might introduce during bottling? I guess if you're bottling from a keg the caps might make a small difference. In any case, after they're capped, the bottles aren't 100% sealed. They can still allow air to get in, albeit very very very slowly.

I believe the yeast only uses ~ 40% of the O2. The caps are also supposed to limit the amount of O2 that diffuses through the cap.Cap on foam.+1 on the Kai Troester Fan Club.

Get about 2000 of them and close yourself in a small room then wet them. If you can't breathe, then they are the right ones.

Are people putting these caps on without sanitizing? I'm not crazy about that idea but there's talk if you sanitize them, then by the time you put them on the bottle, they have lost their O2 absorbing ability.

Somewhere around 2-3 years ago, James from Basic Brewing Radio asked the producer of the O2 absorbing caps about that, and he said that the reaction is very slow, and after they get wet, it takes about 24 hours before they start the O2 absorption. So as long as you only sanitize the caps you are going to use, you will not have a problem with the caps losing their ability.

There is a serious dearth of reliable information regarding the O2 caps out there. I emailed a couple of manufacturers/distributors looking for info/spec sheets on their O2 caps. If I get any responses I'll be sure to share.

FWIW, I don't mind spending a little extra $ for the peace of mind. My SOP is to put them in a bucket of Star San right before I start bottling. They're probably wet for about 1/2 hour or so. I have a hard time believing that's going to be enough to kill their O2 absorbing properties, but if I have to choose between sanitizer or O2 absorption, Star San is going to win every time.